Doctor blade



Jy 23, 1946. v v. CARLSEN ETAL 2,404,539

DOGTOR'BLADE Filed Jan. 15, 1945 Patented July 23, 1946 rI faftville; Conn., assigners to The Aspiriook Corporation, Jewett City, Conn., `a corporation' of l V Delaware Applicaticn January 16, 1945,-seria1No. 572,998A

Thepresent invention relates to Ydoctor blades for use in textile printing machines and similar usesyf" More particularly, l it relatesto a doctor blade that is protected from corrosion from the action 'of the constituentscflt'he printing pastes used'inj such printing, and which may be sharpenedwhen such doctor becomes corroded without undue wear from the sharpening operation.

In printing textile fabrics, a copper roller that is engraved with thed'esign `,to be printed rotates against apress cylinderand prints the design upon a' cloth passing over the cylinder. The color paste'issupplied by `a `furnisher roll that rotates againstfthe engraved copper roller. |Ihe furnisherroll rotatesn` afont containing the'printing pasteand,v as it contacts the engraved roll, deposits the color thereon. The engraved roll, however, when it rotates against the cloth to be printed, should have this color paste only in the depressions of the engraving,"b`ut thefurnisher roll deposits color not only in the'engraving but also wherever it contacts the engraved roll,` both within andwithout the engraved design throughout its'lenfgth. Accordingly, a sharp doctor blade is provided to `clean the engraved roll, that is, to scrape off all the paste deposited thereon except where it is contained in the intaglio design.

This doctor blade is a razor sharp steel blade which is kept pressed against the engraved roll and which scrapes the excess paste therefrom so that it ilows back into the font.

In general, textile fabrics are printed with vat colors, commercial colors (basics and alizarine) or aniline blacks. In printing with vat colors, the paste is alkaline whereas with commercial or aniline colors, the paste is on the acid side. 'I'hese pastes are very corrosive and especially so the anilines, so that the edge of the doctor blade becomes eroded and uneven and unsuitable for performing its function.

As a result of this the doctor blade must be removed from the machine and refiled to sharpen its edge some times several times during a days operation. This causes considerable loss of time in printing. Moreover, no matter what kind of paste is used, the moisture in the paste and in the air will have a corrosive action on the doctor blade, and it is common practice to remove all doctor blades at night and, before setting up the machines in the morning, all doctors must again be led to a razor sharp edge and replaced, an operation that takes ordinarily an hour or two, all depending upon the number of rollers used.

These doctor blades are made of the best quality of medium tempered steel. They vary in l Claim. (C1. lOl-#153) width from two to three inches, in thickness from to als of aninch, and in length according Ato the length of the engraved roller, beingusually some two inches longer. Their top or working edge, i. e., the edge that contacts therollentis filed to a suitable bevel and then sharpened by hand with anoil stone to a Vrazor-like keenness. Their bottom edges `are rmly clamped betweentwo brass holdersor one ofbrassand `one of4 iron, tightlyscrewed together and furnished at` each end with a supporting pivot that rests on a bracket attached to the bearingrof the rollen anda D-, jecting lever by means of weights or screws serves topress the blade on the roller.

In` order to prevent the unequal wearing of their sharp edges, which would occur if they were allowed'to rest continuously in one position on the roller, the doctor blades are given a fslight :to and iro movement in a direction parallel to the axis of the roller. Notwithstanding all theseprecautions, however, the edge ofthe doctor blade in a comparativelyI short time becomes uneven dueto corrosionr and when this happens, streaks oit color` pass under the doctor and cause smears uporithe cloth that is being printed. Theythen must be removed and resharpened.

Here, again, frequent sharpening of the doctors causes a Wearing down and nally a Wearing out of the blades. In sharpening, the printer not only goes over the bevelled face of the doctor with a file and stone, but he also must face it, that is, he must file and stone the bearing face that rests on the roller. This facing or filing of the bearing face wears down the original thickness of the blade and, after a certain amount of such wear is reached, the doctor blade must be discarded as it no longer will fulll its purpose.

`The sharpening or getting up of the edge of the doctor blade is one of the most difficult and most important parts of the machine printers work. The quality of this edge depends not only upon the weight and scale of the engraving but also upon the thickness and hardness of the doctor blade, the angle at which' it rests upon the roller, the pressure applied to it, and upon both the viscosity and density of the printing color which it has to clean oi. Generally speaking, the edge of the Well sharpened cleaning doctor is perfectly straight, absolutely smooth throughout its entire length, and bevelled to a rather obtuse angle. It is sharp as a razor and any roughness, unevenness or the slightest break in the edge is suicient to allow color to escape under it with the result that the nished print under the sharpening operation and that as a;

consequence retains its thickness and hence its eiliciency over a very long period of time.

By use of the doctor bladesof'the present invention, frequent resharpening is unnecessaryV and furthermore the doctor blade may be left in place on thev printing machine all night andthe Work of printing can be resumed immediately in the morning. This results in a saving of many hours a day in printing operations and a substantially greater output of workfrom each machine.

-Brieily`"described, the invention consists of providing ay doctor blade having an edge bevelled in theusual manner to an obtuse angle and sharpenved'toa razor edge and having the face of the blade, that is, that side of the blade that rests on the roller', plated With a hard, smooth, corrosionresisting metal such as chromium or tantalum. Theplatingis carried to the razor edge of the doctor blade on the bearing side so that the corrosive acids in the printing paste do not alect the steel edge of the blade. On the other hand, if afterl use, some small amount of corrosion ofthe edge of the doctor'does take place, the master printer may remove it and V-resharpeh it in the usualmannersin'ce' the bevelled face of the'blade is not'plated. The-plated side of the blade, however,'wil1 not wear under this sharpening, as the platingefgives a very hard and smooth surface on which the file and stone will glide Without biting into .the metal. Thecoatings used forV this purpose should be metals that are not only resistant to. thepactionjof acids. but should have a very. hard-smoothsurface so that the bearing face cannotbe led vor stoned. When so coated, the

which the blanket 2 is iap'p'ed. The cloth 3 which is being printed passes between the blanket 2 and the engraved roll 4. The furnisher roll 5 rotates jin Vthefont 6 andcontacts the engraved roll 4 a adapted andarranged to bear on a of atextile printing machine. d A. n... v VIGrGrOA CARLSEN. Y,

ALWIN HEINRICH.

which rotates in reverse direction to the rotation of furnisher roll 5. 'I'he doctor blade 'I' presses with' its plated face I 0 bearing against the engraved rollfd, thus scraping the color from said roll except where it fills the depressions of the engraving.

In Fig. II is shown the doctor blade With its holder or sheath 8, its steel body 9 and chromium or tantalum plating l0 on one side of the steel body.v Y L It will be apparent that when a doctor of the present invention is sharpened by the printer,l

only the bevelled side of the blade Will be filed and.AV Y

stoned, as neither the le nor the stone will make any impression on the hard, smooth chromium or tantalum coating on the bearing Aface. Asa result; there will be little wear on the platedface and thersurface on that side will always remain the same without loss of thickness of the blade. Such a plated doctor blade will have a life several times as long as the ordinary doctor blades now in use and in addition Will retain its sharpness much longer, thus requiring fewer sharpenings.

Having thus described our invention, what wel claimis: Y 4 1 A doctor blade comprising a steel backing beveled down to a razor sharp edge and a plating.

of chromium on the unbeveled underside extending to the edge, the plated side of said edge being printing roller. 

